1. Field of the Invention
The present invention relates a sync signal detection method preferably used for a communication system of a radio LAN which connects a plurality of terminals through radio and a radio communication system to the sync signal detection method.
2. Description of the Related Art
Because a data processor system such as a computer system is advanced in function, it is frequently performed to share a file or data by connecting a plurality of computer systems and thereby constituting a LAN (Local Area Network) or transfer electronic mails and various types of data. A conventional LAN connects computer systems each other by using a coaxial cable or twisted pair cable.
However, because the LAN using a cable requires wiring operations, it is difficult to easily constitute the LAN and a cable for connecting computer systems to each other is an obstacle. Therefore, a radio LAN is noticed as a system for releasing a user from wiring of a conventional LAN according to a cable system.
In this case, the data transmitted between computer systems is data having a comparatively high transmission rate. Therefore, it is proposed to transmit data through a high-efficiency transmission system such as OFDM (Orthogonal Frequency Division Multiplex) system or CDMA (Code Division Multiple Access) system.
Specifically, because use of information as multimedia has been recently accelerated, data including a large amount of content such as image data or audio data has been frequently used. Therefore, it is also requested for a radio LAN to improve a transmission rate so that data including a large amount of content such as image data or audio data can be transmitted and it is proposed to use the above-described high-efficiency transmission system.
However, when increasing a transmission rate, it is necessary for a terminal for receiving transmitted data to securely perform sync acquisition processing in order to correctly perform demodulation in the terminal.
A sync signal for sync acquisition is added to transmitted data and demodulation is executed at the reception side on the basis of the timing when detecting the sync signal. Therefore, when a reception-side terminal fails in acquisition of the sync signal, it is impossible to receive and demodulate the transmitted data before the next sync signal is acquired. When the above trouble occurs, a request for retransmission of data is necessary and a prepared transmission band is wastefully used and a network using efficiency is deteriorated.
In view of the above, the object of the present invention is to make it possible that when performing that kind of radio communications setting of sync timing can be preferably performed by detecting a transmitted sync signal.
A sync signal detection method of the present invention uses a sync signal detection method for receiving a sync signal regularly radio-transmitted from a predetermined station at a predetermined cycle and detecting the received sync signal, comprising the steps of judging a cycle at which a sync signal is detected, setting a detection window having a predetermined width every judged cycle, and judging only a sync signal detected from received signals in the detection window as an effective sync signal.
According to the sync signal detection method, it is possible to perform sync processing by using a cyclically-set detection window and thereby using only a sync signal transmitted in a certain range and minimize a sync-timing delay at the side for receiving a sync signal even if the timing for transmitting a sync signal is comparatively greatly delayed due to relay processing.
Moreover, a radio communication system of the present invention comprises reception means for receiving a radio signal, sync detection means for detecting a predetermined sync signal out of radio signals received by the reception means, cycle judgment means for judging a cycle at which a sync signal is detected by the sync detection means, and sync control means for setting a sync detection window at a cycle judged by the cycle judgement means and judging only a sync signal detected by the sync detection means in a range in which the window is set as an effective sync signal.
According to the radio communication system, only a sync signal detected by the sync detection means in a sync detection window set by the sync control means is judged as a correct-timing sync signal and sync processing is performed by using only the sync signal judged as the correct-timing sync signal.